A systematic study on the Horner-Wadsworth-Emmons (HWE) reaction has shown that ethyl diphenylphosphonoacetate and methyl diphenylphosphonoacetate give a high excess of (Z)-alkenes. These reaction conditions were then used to prepare (Z)-ethyl-5-phenylpent-2-enoate, the corresponding (E)-isomer being prepared by standard Wittig chemistry. Reduction of each allylic ester, with diisobutylaluminium hydride (DIBAL), gave the allylic alcohols (15) and (19), respectively. Epoxidation of (15) and (19), under Sharpless conditions, gave separate samples of all four stereoisomers of 2,3-epoxy-5-phenylpentan-1-ol. Esterification of each isomer with Cbz-valine, under Mitsunobu conditions, provided (9)-(12) which were assayed against HIV protease. The cis series (9)-(10) proved to be significantly more potent than the trans (11)-(12) and, within each of these series, the isomers derived from L-diisopropyltartrate [(9) and (11)] were the most active.
An efficient one-pot method for the syntheses of di- and polybrominated estersfrom readily available aldehydes is reported. The direct use of the in situ generated byproduct PPh3O in the following reactions greatly improves the efficiency of the cascade. Also, the substrate scope of the reaction is proved to be broad.
Recycling the Waste: The Development of a Catalytic Wittig Reaction
作者:Christopher J. O'Brien、Jennifer L. Tellez、Zachary S. Nixon、Lauren J. Kang、Andra L. Carter、Stephen R. Kunkel、Katherine C. Przeworski、Gregory A. Chass
DOI:10.1002/anie.200902525
日期:2009.9.1
It's all in the ring: 3‐Methyl‐1‐phenylphospholane‐1‐oxide (4–10 mol %) and an organosilane reducing agent are the key components in the first Wittigreactioncatalytic in phosphine. The protocol also functions well on larger scale: a reaction on a 30 mmol scale yielded 3.39 g of product, corresponding to a yield of 67 %.
Intermolecular Coupling of Alkynes with Acrylates by Recyclable Oxide-Supported Ruthenium Catalysts: Formation of Distorted Ruthenium(IV)-oxo Species on Ceria as a Key Precursor of Active Species
A solid ceria-supported ruthenium catalyst (Ru/CeO2) as well as a zirconia-supported ruthenium catalyst (Ru/ZrO2) showed high activities toward the intermolecular coupling of alkynes with acrylates to give the corresponding 1,3-dienes in high yields. The reaction proceeded in the presence of sodium formate and both internal or terminal alkynes and norbornene could be applied for the catalytic systems
固体二氧化铈负载的钌催化剂(Ru / CeO 2)和氧化锆负载的钌催化剂(Ru / ZrO 2)对炔烃与丙烯酸酯的分子间偶联显示出高活性,从而以高收率得到相应的1,3-二烯。反应在甲酸钠的存在下进行,内部或末端炔烃和降冰片烯均可用于催化体系。固体钌催化剂可以循环使用几次,而不会显着降低活性。二氧化铈负载的钌催化剂的FT-IR和X射线吸收精细结构(XAFS)研究表明,二氧化铈上扭曲的钌(IV)-氧代物种在反应的初始阶段就转变为低价钌物种对偶联反应有效。
Amide cuprate reagents as a new class of nitrogen nucleophiles. Application to asymmetric synthesis of .beta.-lactams